🧪 Petroleum Ether-Extractable Substances

Physicochemistry PN-C-04559

Overview

Petroleum ether-extractable substances (PEES) include group of organic compounds extractable from water and wastewater using petroleum ether (extraction gasoline, fraction 40–60°C). This group includes: petroleum substances (hydrocarbons, mineral oils), animal and vegetable fats, waxes, resins, fatty acids, and other non-polar compounds. PEES parameter is summary indicator of organic contamination of wastewater.

Polish standard PN-C-04559 describes gravimetric method — water sample is acidified and extracted with petroleum ether, extract is evaporated, and dry residue weighed on analytical balance. Method is simple, does not require expensive apparatus, but is time-consuming and less selective — does not distinguish petroleum substances from fats.

Difference between indicators: PEES includes ALL non-polar substances (petroleum + biogenic), while hydrocarbon oil index (PN-EN ISO 9377-2, GC-FID) includes ONLY C10–C40 hydrocarbons after polar substance removal. In practice: PEES > HOI, because PEES contains fats, esters, etc.

PEES parameter is required in water permits, municipal and industrial wastewater control (meat plants, dairies, refineries, auto workshops), and fat and oil separator effectiveness assessment.

Method principle

Wastewater sample (0.5–1 L) is acidified with hydrochloric or sulfuric acid to pH < 2, ensuring transfer of fatty acids and soaps to free (non-ionic) form, extractable with ether. Acidified sample is extracted three times with petroleum ether (fraction 40–60°C) in separatory funnel or by continuous extraction in Soxhlet apparatus. Combined ether extracts are dried with anhydrous sodium sulfate, evaporated on rotary evaporator or in water bath (under fume hood), and dry residue is dried at 105°C (30 min) and weighed on analytical balance with accuracy ±0.1 mg. Result expressed in mg/L.

Applications

• Municipal and industrial wastewater quality control (water permit)
• Wastewater from food plants monitoring (dairies, meat plants, slaughterhouses)
• Wastewater from refineries, fuel stations, auto workshops control
• Fat and oil separator effectiveness assessment
• Landfill leachate testing
• Surface water monitoring — fat and oil contamination

Key parameters

Standard

Standard number

PN-C-04559:1982

Title (PL)

Woda i ścieki — Badania zawartości substancji ekstrahujących się eterem naftowym

Title (EN)

Water and wastewater — Determination of petroleum ether-extractable substances

Step-by-step procedure

1. Glassware preparation

   Wash 250 mL round-bottom flasks with acetone and petroleum ether. Dry at 105°C (30 min). Cool in desiccator. Weigh with accuracy 0.1 mg (mass m₀).

   ⏱ Time: 45 min • 🌡 Temperature: 105°C

2. Sample acidification

   Measure 1 L wastewater sample. Acidify with HCl to pH < 2 (check with indicator paper). Mix 5 min.

   ⏱ Time: 10 min

3. Extraction I

   Transfer acidified sample to 2 L separatory funnel. Add 50 mL petroleum ether. Shake vigorously 3 min (carefully — vent). Let phases separate (15 min).

   ⏱ Time: 20 min

4. Extraction II and III

   Drain aqueous phase. Repeat extraction twice with 50 mL petroleum ether each. Combine all organic phases.

   ⏱ Time: 40 min

5. Extract drying

   Pass combined ether extracts through funnel with 20 g anhydrous Na₂SO₄. Collect in pre-weighed round-bottom flask.

   ⏱ Time: 10 min

6. Solvent evaporation

   Evaporate petroleum ether on rotary evaporator (water bath 40°C, vacuum). Or evaporate under fume hood in water bath. Do not overheat — volatile substances may be lost.

   ⏱ Time: 30–60 min • 🌡 Temperature: 40°C

7. Residue drying

   Place flask with residue in oven at 105°C for 30 minutes. Cool in desiccator to room temperature (30 min).

   ⏱ Time: 60 min • 🌡 Temperature: 105°C

8. Weighing

   Weigh flask with residue (mass m₁) with accuracy 0.1 mg. Repeat drying and weighing to constant mass (difference < 0.5 mg).

   ⏱ Time: 10 min

9. Calculations

   PEES [mg/L] = (m₁ - m₀) × 1000 / V_sample [L], where m₁ — flask mass with residue, m₀ — empty flask mass, V — sample volume.

   ⏱ Time: 5 min

10. Quality control

    Blank (clean water through entire procedure) < 0.5 mg/L. Duplicate: RPD < 25%. Spike with mineral oil — recovery 70–120%.

    ⏱ Time: 30 min

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Petroleum ether — highly flammable (flash point < -20°C), vapors heavier than air — EXCLUSIVELY in fume hood!
• Petroleum ether vapors — narcotic at high concentrations, irritant to respiratory tract
• Hydrochloric acid — corrosive, irritant vapors, eye and hand protection
• Wastewater samples — potentially infectious, nitrile gloves and face protection
• Rotavapor with water bath — do not exceed 40°C when evaporating ether
• Collect ether waste in sealed flammable organic waste container

Frequently asked questions